Optimized Design of a Dynamically-Based Motion Generating Spatial Four-Bar Mechanism on Rigid Multibody Systems

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Addis Ababa University


The four-bar spatial mechanism is the most basic chain that can be composed of four links and can include joints with any combination of rotational and translational freedom used in thousands of applications. This thesis will present some of the techniques and introduce solution tools that were not needed for planar motion. One of the new techniques known as the Euler parameters will be considered in this work. The thesis includes modeling, optimizing computer-aided dynamic analysis and simulation of four-bar spatial mechanism composed of rigid bodies that are used for different applications of spatially moving motion generating mechanisms. The Motions of the rigid bodies are predicted by numerically integrating Differential-Algebraic Equations (DAEs) developed from principles of mechanics by the Newton-Euler’s approach. The computer program, MSC.ADAMS2005 will be used to model, solve, simulate, and optimize the dynamics of the appraised spatial four-bar mechanism as a lens-polishing mechanism by integrating the differential equations. Unlike analytical synthesis, optimization allows direct incorporation of a greater number of design constraints, thus resulting in solutions that are more practical. In this thesis, an efficient algorithm known as the Generalized Reduced Gradient (GRG) is used to synthesize all kinematic linkages of the spatial mechanism. This approach will allow monitoring and controlling objectives and constraints, which will yield practical solutions to realistic mechanism design problems with lower kinematic pairs. In addition to the above mentioned points, a mobility analysis has been done for the RSSR mechanism, which is a one degree of freedom, single loop, and spatial mechanism. Thus, this thesis specifically discusses a practical example of a lens polishing four-bar spatial mechanism that simply substitutes the extremely expensive existing polishing robots. This mechanism is applicable in polishing lenses of military fire control instruments found in the Ethiopian Defence Forces. Thus, the design presented in this thesis provides a relatively low-cost solution for the existing problem as compared to the robots. This can be created with ease of manufacture in a machine shop quickly and simply. Numerical results obtained in this thesis are compared with existing literatures.



Spatial Four-Bar Mechanism, Dynamically-Based Motion, Optimized Design, Rigid Multibody Systems